Light Signaling, Root Development, and Plasticity

Abstract

Light signaling can affect root development and plasticity, either directly or through shoot-root communication via sugars, hormones, light, or other mobile factors.

Figure 1.

Relative amounts of photoreceptors in Arabidopsis tissues. The graph displays the relative expression of photoreceptors across seedling tissues. Both gene expression and protein (when data are available) abundance are shown. The box that groups classes of receptors indicates that intensities within can be compared. In the PHY box, “L” stands for protein levels in light and “D” for protein levels in the dark. Source data: for all, BAR eFP browser (http://bar.utoronto.ca/efp/cgi-bin/efpWeb.cgi), PHYs (Somers and Quail, 1995; Goosey et al., 1997; Tóth et al., 2001; Sharrock and Clack, 2002; Salisbury et al., 2007), PHOTs (Sakamoto and Briggs, 2002; Moni et al., 2015), CRYs (Tóth et al., 2001), and UVR8 (Rizzini et al., 2011).

Figure 2.

Root growth is affected by light quantity and quality. A, Eight-day-old seedlings grown on half-strength Murashige and Skoog medium in darkness and white light (WL; 140 μm m⁻² s⁻¹ photosynthetically active radiation). B, Eight-day-old seedling grown in white light (140 μm m⁻² s⁻¹) or white light plus FR (WL+FR; R:FR 0.1). The arrowheads point to the root-shoot junctions.

Figure 3.

The aboveground regulation of root development in dense vegetation involves photosynthesis, light piping, hormones, and mobile factors. The primary effect of light is to enable photosynthesis, which leads to the production of sugars (sucrose) that enable the root to grow. Photomorphogenic development is associated with the production of auxins in the shoot, which are transported rootward and enable root development. HY5 is stabilized in the shoot during photomorphogenesis and is transported rootward, where it regulates nitrate uptake and root development. Light is used as a cue to detect neighboring plant competition via sensing of the R:FR ratio. Plant tissues reflect FR, which lowers the nearby R:FR ratio, leading to shade avoidance responses mediated by, among others, auxin and GA. These hormones can be transported rootward, where they affect root development. There also are indications that shade avoidance responses, in a negative feedback mechanism, decrease the amount of rootward auxin transport. FR light itself also can be transmitted directly through woody, vascular tissues from the shoot to the root, where it can affect root-localized PHYs. Plant vector drawing: Lobet (2017).